1. Field of the Invention
The present invention relates to a technology for effecting grounding connection between an object of connection continuous with a metal portion of an electronic component or the like contained in an electronic apparatus such as a mobile phone, a personal digital assistant, a mobile music player, or a vehicle-mounted apparatus, and an object of connection continuous with another metal portion.
2. Description of the Related Art
Some mobile electronic apparatuses such as a mobile phone and a personal digital assistant use an electronic component and a member having metal portions. When a mobile electronic apparatus has metal portions, there is a fear of a difference in potential being generated between one metal portion and the other metal portion and noise being generated within the electronic apparatus, and hence it is necessary to effect grounding connection between the metal portion and the other metal portion.
As technologies related to this grounding, there are known, for example, the following three conventional technologies. According to the first technology, which is disclosed in JP 2004-4093 A, there is used a sponge with conductive cloth formed by cylindrically wrapping a conductive cloth formed of a non-woven cloth or knitted cloth using conductive yarns around a core material with flexibility such as sponge. In the second technology, which is disclosed in JP 2003-347755 A, there is used a grounding spring formed of a metal piece. In the third technology, which is disclosed in JP 2003-347755 A, there is used a columnar conductive silicone elastomer member in which a conductive filler such as silver particles is uniformly dispersed all over.
The sponge with conductive cloth of the first technology is press-held between a metal portion of a casing and a grounding portion of a circuit board. It should be noted, however, that it is rather difficult to press-hold a small sponge with conductive cloth between the casing and the board at a predetermined position. Further, due to its rather poor dimensional precision, the size of the sponge sometimes exceeds the accommodation space acceptable for the mobile electronic apparatus, which is required to be as small as possible. Further, it only allows production in a simple configuration such as a rectangular prism, and hence it cannot be applied to ground connection which involves a complicated configuration.
The grounding spring of the second technology, which is formed of a metal piece, is also press-held between the metal portion of the casing and the grounding portion of the circuit board. However, the small grounding spring, which is formed of a metal piece, is subject to deformation, and when it is excessively deformed, it cannot be restored to the former shape, thus failing to perform ground connecting function. Further, the grounding spring is held in point contact with the ground connecting portion, and hence it is not always to be expected to exhibit a sufficient conduction characteristic.
The silicone rubber of the third technology is also press-held between the casing metal portion and the grounding portion of the circuit board. It should be noted, however, that it is rather difficult to press-hold the small columnar conductive silicone rubber member between the casing and the board at a predetermined position. Further, for the conductive silicone rubber to provide a satisfactory conduction characteristic, it is necessary to uniformly disperse a large amount of conductive filler in the silicone rubber serving as the base material. However, when the amount of conductive filler is larger, the silicone rubber becomes rather hard, fragile, and subject to chipping.